This study of neurotransmitters and drugs presently focuses on characterization of neurotransmitter receptors. The dopamine receptor has been labeled with 3H-dopamine, 3H-haloperidol, 3H-dihydroergokryptine, and 3H-apomorphine. Changes in the number of receptors have been evaluated in various conditions including denervation and chronic neuroleptic treatment. The GABA receptor has been characterized by the binding of 3H-GABA and 3H-bicuculline. The glycine receptor has been studied with 3H-strychnine. The norepinephrine alpha-receptor has been labeled with 3H-WB-4101, 3H-clonidine, 3H-epinephrine, 3H-norepinephrine, 3H-dihydroergokryptine. Interactions of alpha-receptors with neuroleptics and tricyclic antidepressants have been evaluated. It has been possible to label both alpha- and beta-receptors with 3H-epinephrine in the same tissue specimens. In the coming year we propose to evaluate characteristics of norepinephrine, glycine, GABA and dopamine receptors in greater detail carrying forward the initial findings of the present year. BIBLIOGRAPHIC REFERENCES: Snyder, S.H. and Yamamurs, H.I. Antidepressants and the muscarinic acetylcholine receptor. Arch. Gen. Psychiat. 34: 236-239, 1977. Enna, S.J., Bennett, J.P., Jr., Bylund, D.B., Creese, I., Burt, D.R., Charness, M.E., Yamamura, H.I., Simantov, R. and Snyder, S.H. Neurotransmitter receptor binding: regional distribution in human brain. J. Neurochem. 28: 233-236, 1977.